Currently available ventricular assist systems using a continuous delivery blood pump, whether intravascular or implanted, have a common problem: somewhere in the system, the drive for the pump blades has to traverse the wall of the blood path. This is equally true of the shaft which drives the impeller of a centrifugal pump such as disclosed in U.S. Pat. No. 4,704,121 and of the drive cable of U.S. Pat. No. 4,625,712 which must traverse the wall of the femoral artery.
Wherever the drive traverses the wall of the blood path, a discontinuity exists which involves a danger of thrombus formation. Although this danger is substantially alleviated in centrifugal pumps by the invention disclosed in U.S. Pat. No. 4,704,121, it still exists in the physiologically much more desirable axial flow pumps.
Ideally, this problem can be solved by an axial flow pump with a magnetically suspended rotor, such as that proposed in copending application Ser. No. 07/036,304, which requires no bearing purge fluid supply and no penetration of the blood path wall; nor, for that matter, any percutaneous device. However, magnetically suspended blood pumps belong to a developing technology, and their commercial viability is still in the future.
A major problem with implanted cardiac assist devices is the almost universal emergence of infection when a device has been implanted for several months. It is believed that infection is related not only to sepsis of the percutaneous access, but also to the weight, relative motion and surface area of the device itself.